Polyvinyl alcohol (PVOH) is a synthetic resin generally prepared by the alcoholysis, usually termed hydrolysis or saponification, of polyvinyl acetate. Fully hydrolyzed PVOH, where virtually all the acetate groups have been converted to alcohol groups, is a strongly hydrogen-bonded, highly crystalline polymer which dissolves only in hot water—greater than about 140° F. (60° C.). If a sufficient number of acetate groups are allowed to remain after the hydrolysis of polyvinyl acetate, the PVOH polymer then is known as partially hydrolyzed, it is more weakly hydrogen-bonded and less crystalline and is soluble in cold water—less than about 50° F. (10° C.). Both fully and partially hydrolyzed PVOH types are commonly referred to as PVOH homopolymers although the partially hydrolyzed type is technically a vinyl alcohol-vinyl acetate copolymer.
The term PVOH copolymer is generally used to describe polymers that are derived by the hydrolysis of a copolymer of a vinyl ester, typically vinyl acetate, and another monomer such as, for example, an ethylenically unsaturated monomer, e.g., 2-acrylamido-2-methyl propane sulfonic acid; see U.S. Pat. Nos. 7,932,328; 7,790,815; 7,786,229 and 6,818,709 all to Vicari. PVOH copolymers can be tailored to desired film characteristics by varying the kind and quantity of copolymerized monomers.
It is known in the art that many PVOH copolymers, because of their structure, can be much more rapidly soluble in cold water than the partially hydrolyzed type of PVOH homopolymers. Such copolymers have therefore found considerable utility in the fabrication of packaging films for the unit dose presentation of various liquid and powdered products including agrochemicals, household and industrial cleaning chemicals, laundry detergents, water treatment chemicals, and the like. However, not all PVOH copolymers have desirable and optimal water solubility to be useful in the fabrication of packaging films for the unit dose presentation of various liquid and non-liquid (e.g. powdered) products or encapsulating these products including fertilizer, agrochemicals, household and industrial cleaning chemicals, laundry detergents, water treatment chemicals, and the like.